Elastic fibers and in particular elastic non-wovens were up to now manufactured from selectively hydrogenated poly(monovinylaromatic/conjugated diene) block copolymer alone or mixtures thereof with other thermoplastic polymers and in particular poly(alkylene) by melt spinning and/or melt blowing techniques. Such techniques and the starting block copolymers to be used were known, e.g. from British patent applications Nos. 2,178,433, 2,197,874, German patent application No. 3625775, U.S. Pat. Nos. 4,789,699 and 4,692,371 and European patent applications Nos. 0030767, 0033569, and 0211466.
The prior art processes clearly had as limitation, that only relatively low molecular weight (Mn.ltoreq.100,000; apparent molecular weight.ltoreq.140,000) selectively hydrogenated block copolymers could be processed, due to melt flow requirements in such equipment.
In particular from European patent application 0033569 a method was described for the production of elastic fibers via the melt-blowing process. The fibers produced by said process were based on a selectively hydrogenated thermoplastic rubber e.g. KRATON G 1652 (KRATON is a trade mark), being a three block copolymer having polystyrene endblocks and a rubbery poly(ethylene-butylene) midblock. According to the teachings of said document, the thermoplastic rubber as such could not be extruded to form fibers and this only could be remedied by blending said thermoplastic rubber with fatty acids, such as stearic acid, in order to solubilize the thermoplastic rubber in the melt phase and to enable the extrusion of it into fibers without the occurrence of melt fracture.
However, in order to enhance the performance of the thus obtained elastic fibers, it was recommended to remove the substantial amount of stearic acid (20% by weight) as their presence impeded the elastic movement of the rubber molecules. A proposed method to accomplish this was to soak the fiber with isopropyl alcohol and this post treatment was not only cumbersome but made said process economically unattractive.
A further improvement of this concept was known from European patent application No. 0211466, disclosing a melt-spinnable or melt-blowable composition, comprising (a) 55 to 85 parts by weight of at least one three block copolymer having two endblocks A and a midblock B, wherein the blocks A were monoalkenyl arene polymer blocks and the B block is a substantially completely hydrogenated conjugated diene polymer block, the number average molecular weight of the or each three block copolymer being in the range of from 16,000 to 175,000, the number average molecular weight of the A blocks being in the range of from 4,000 to 30,000 and the monoalkenyl arene content of the or each three block copolymer being in the range of from 10 to 50% by weight of said three block copolymer, and (b) from 15 to 45 parts by weight of at least one two block copolymer C-D, wherein the C block is a monoalkenyl arene polymer block having a number average molecular weight in the range of from 4,000 to 30,000, and the D block is a substantially completely hydrogenated conjugated diene polymer block, having a number average molecular weight in the range of from 25 to 75% of the number average molecular weight of the midblock B of the or each three block copolymer, and wherein the total parts by weight of said three block copolymer(s) and of said two block copolymer(s) in said composition equals 100 parts by weight.
Although in page 5 of said European patent application, there was indicated that the total number average molecular weight of these three block copolymers and especially the upper limit thereof was primarily dictated by the at that time available equipment and should be at most 175,000 (apparent molecular weight 250,000), in the examples significantly lower number average molecular weight triblock copolymers were used (M.sub.n in the range from 33,000 to 70,000).
From the European patent application No. 0525628 was known a composite fiber having a single filament fineness of not more than 8 deniers and comprising a protective polymer component (A), comprising a fiber-forming thermoplastic polymer, and a polymer component (B) containing a large amount of an inorganic fine powder, said component comprising a hydrogenated block copolymer comprising poly(vinyl aromatic) blocks and poly(conjugated diene) blocks and containing a specific phenol based compound (in particular hydroxy tert-butylphenyl compounds of depicted formula I therein). It will be appreciated that in particular with reference to Table 1 therein, the number average molecular weights of the complete triblock copolymers to be used to form the core of the composite core/shell fiber were in the range of from 50,000 to 100,000, i.e. relatively low number average molecular weights only.
Moreover, said fibers could not be regarded as elastic fibers, the object of the present invention, whereas the mechanical properties of said composite fibers were mainly stipulated by the type of the shell forming polymer component (A) preferably being polyester.
On the other hand, gel spinning processes for the manufacture of yarns and fibers, showing attractive tensile strength and stiffness, from polymers which were completely different from hydrogenated block copolymers were known from e.g. European patent applications Nos. 519359, 398434, 360358, 349146, 327696, 324135, 310171, 144793, 139141, 105169, 0056875 and U.S. Pat. No. 4,137,394 and PCT applications WO 90/14453, WO 92/10524 and WO 92/10600.
It will be appreciated that there is existing a growing need for higher tensile strength elastic articles, such as industrial fibers or yarns, derived from substantially pure, relatively high molecular weight block copolymers, i.e. having number average molecular weights more than 70,000, preferably more than 120,000, and more preferably more than 180,000, (corresponding to apparent molecular weights of 100,000, 170,000 and 255,000 respectively), derived from monovinyl aromatic monomers and conjugated diene monomers, the poly(conjugated diene) internal blocks of which have been selectively hydrogenated. However, it has appeared not possible up to now to prepare such desired fibers, yarns, or films by using conventional process methods from pure high molecular weight selectively hydrogenated block copolymers, i.e. free of the conventionally used processing aids and more in particular extender oils, which appeared to deteriorate the polymer properties in a certain degree.
Therefore it was an object of the present invention, to provide said desired high tensile strength elastic articles and in particular industrial fibers, yarns, or films derived from substantially pure selectively hydrogenated block copolymers of relatively high molecular weight.
A further object of the present invention was to provide a manufacturing process for said high tensile strength elastic articles such as industrial fibers, yarns, or films.